Abstract: Method for obtaining a biodiesel in a continuous system from vegetable oils of variable degree of acidity, whereby, in a first step, a specific blend of vegetable oils of variable degree of acidity and methanol or ethanol are subjected to pressure and to heat in a multiple and continuous horizontal modular tube reactor, in the presence of a strong acid as catalyst, until a vegetable oil with an acidity of less than 1% is obtained. In a second step, this oil is transesterified by being blended with sodium or potassium methoxide, the glycerol being separated out, leaving glycerol on the one hand and, on the other, biodiesel, which, once purified and scrubbed, will be suitable for use in engines. The number of modules, both in the first and in the second step, is a function of the system's capacity.